On 03/22/2016 06:40 AM, Antony Pavlov wrote: > On Tue, 22 Mar 2016 00:02:57 +0100 > Matthias Schiffer <mschiffer@xxxxxxxxxxxxxxxxxxxx> wrote: > >> Hi, >> we're experiencing weird nondeterministic hangs during bootconsole/console >> handover on some ath79 systems on OpenWrt. I've seen this issue myself on >> kernel 3.18.23~3.18.27 on a AR7241-based system, but according to other >> reports ([1], [2]) kernel 4.1.x is affected as well, and other SoCs like >> QCA953x likewise. >> >> See the log below for the exact place it hangs; the log was taken in during >> a good boot; a bad boot will just hang forever at the marked location. The >> issue is extremely hard to debug, as changing the timing in any way (like >> adding additional printk) will usually make it work without problems. (Even >> recompiling the kernel with the same config, but different uname timestamp >> will make the occurence more or less likely) >> >> My theory is the following: >> >> As soon as ttyS0 is detected and installed as the console, there are two >> console drivers active on the serial port at the same time: early0 and >> ttyS0. I suspect that the hang occurs when the primitive early0 >> implementation prom_putchar_ar71xx waits indefinitely on THRE, > > Can you use EJTAG to prove your theory? > > -- > Best regards, > Antony Pavlov > Unfortunately, the board I can reproduce this at the moment does not have an accessible JTAG port. I hope I can reproduce it on other hardware which is more developer-friendly, but no luck so far. Matthias
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